This invention relates to an apparatus for and method of detecting the degree of deterioration of lubricating oil used in an internal combustion engine and, more particularly, to such an apparatus utilizing a pair of spaced apart electrodes dipped into the lubricating oil to form a sensor capacitor having a capacity that varies as a function of the lubricating oil dielectric constant.
When lubricating oil becomes deteriorated its lubricating ability is reduced due to contaminants, such as soot, which mix with the oil during use in an internal combustion engine. It is desirable to know the lubricating oil contamination state to signal when the oil should be changed.
In order to determine the degree of deterioration of lubricating oil, it has been the practice in the past to measure the conductivity of the lubricating oil by sensing current flow between a pair of electrodes dipped in the lubricating oil within an oil pan. However, the conductivity of lubricating oil varies to such an extent with oil temperature and brand as to completely invalidate the expected relationship between the lubricating oil conductivity measurement and the lubricating oil degree of deterioration. This is true particularly for diesel engines where a great amount of soot enters lubricating oil.
Therefore, the present invention provides an apparatus for and method of detecting the degree of deterioration of lubricating oil with greater accuracy independently of lubricating oil temperature and brand. Applicants have found that variations in the capacity or impedance of a sensor capacitor comprised of a pair of spaced apart electrodes dipped into lubricating oil corresponded relatively accurately with the extent to which the lubricating oil is deteriorated. The present invention utilizes the variations of the sensor capacitor as an indicator of oil deterioration.